1. Field of the Invention
The present invention relates to an image read device of a reduction optical system for inputting image data, such as digital copying machine, facsimile, and printer, and more particularly to an image read device of the reduction optical system for inputting image data projected from a film projector.
2. Description of the Related Art
There has been proposed a copying machine with an image read device of the reduction optical system. This type of the image read device is made up of an exposure lamp for radiating an original to form an optically read image (optical image), a mirror unit for transmitting the optical image, which includes a full rate mirror (FRM) and a half rate mirror (HRM), and an optical lens for reducing the size of the optical image transmitted through the mirror unit and focusing it on an organic photosensitive belt.
Recently, digital color copying machines have been studied and developed. The applicant of the present patent application also proposed an inventive digital copying machine in Japanese Patent Application No. 63-292195, for example. The proposed digital copying machine is provided with an image input terminal (IIT). The IIT optically reads an image on an original in terms of three primary colors, red (R), green (G), and blue (B), and converts optical image information of those colors into electrical digital signals representative of optical density.
The IIT is made up of an imaging unit, a drive means for moving the imaging unit, and an electrical hardware. The imaging unit includes an exposure lamp, a rod lens array for reading an image on an original, and a CCD line sensor, and optically reads the image by scanning the original. The hardware applies converting processing to the read signals derived from the CCD line sensor.
Since the digital color copying machine digitally processes the image signals, various types of processings can easily be performed, and therefore provides color copies of high quality.
In the digital color copying machine, attempt has been made to make a copy of an image recorded in a film, as disclosed in Japanese Patent Application No. 63-299359, filed by the present applicant.
The imaging unit of the IIT in the digital color copying machine is of the closed type, and hence its structure is relatively large. In the light of space saving, it is desirable that the size of the device is as small as possible.
To this end, the possibility exists that the image read device of the reduction type is applied for the IIT of the digital color copying machine. In designing a digital copying machine based on the possibility, if the film projector is simply used, the resultant color copying machine uses two optical lenses, an optical lens in the film projector and an optical lens for focusing an image in the IIT. As a result, a modulation transfer function (MTF) of a copy of a film image from the film projector is reduced.
In such a copying machine, a mirror unit is additionally used which is for projecting a film image on a platen glass by the film projector. Because of this mirror unit, the size of the film projector is proportionally increased.